As coal is mined, a large amount of methane gas accumulates in the coal mines. Sometimes this methane gas is simply burned off. At other times, it is allowed to accumulate. This invention relates to the field of the recovery of methane gas from a coal mine. More particularly, it involves an apparatus and method for economically recovering methane gas from a coal mine and transporting the methane gas to an end user.
Much attention has recently been focused on emission standards, particularly for high volume public utilities such as power plants. Power plants commonly use cofiring boilers to produce electricity. However, much of the coal available in the United States has high contents of Sulfur Dioxide or Nitrogen Dioxide, two substance emissions which are particularly undesirable for the environment. Many environmental regulations require the reduction of the use of high sulfur content coal in public utilities. One alternative to meeting these emission standards is to pay a penalty for such sulfur dioxide emissions. It is an object of this invention to provide an economical alternative to the payment of these environmental penalties due to the burning of Sulfur Dioxide laden coal.
Many coal boilers which provide Sulfur Dioxide, Nitrogen Dioxide, and GHG emissions are currently in use in the United States. However, these boilers may be easily converted to a cofiring system at a low capital cost. This ease of conversion, along with the economic value of the converted system, makes cofiring coal with gas a low risk approach to using coal mine gas as a substitute for coal. Cofiring with gas improves ash quality, reduces slag build-up, and can slightly increase boiler efficiency. The gas fuel input may vary from less than 3% to 100% of the total fuel input, increasing the short term peaking capability of the coal fire burner.
Approximately 370 utility boilers now have cofiring capabilities, many of which are situated near gassy coil mines. Gassy coal mines are coal mines in which a large amount of methane gas exists. The methane gas is adsorbed by the underground coal and seeps out in salvageable quantities.
In order to determine which boilers would be ideal for cofiring with coal mine gas, operators must consider the gas demand and availability, pipeline distances, and boiler conversion costs. Because coal firing is an ideal application for variable quality coal mine gas, the U.S. EPA is researching the economic potential to site new cofired boilers at gassy coal mines to employ coal, coal mine gas, and ventilation air as fuels. One other alternative to siting these boilers at or near gassy coal mines is to develop an economical way to recover the methane gas from the mine and economically transport it to already existing boiler sites.
It is another object of this invention to provide an alternative means of transportation for coal mine gas, involving a set of specially prepared tankers to transport the methane coal mine gas from the mine to the consumption site.
While cofiring gas at cofired industrial and utility boilers is economically compelling, heretofore there have been great difficulties encountered in the transportation of the coal mine gas to suitable end-user facilities. If a method could be devised to economically capture coal mine gas into tanks and if transportation costs could be held down, the economics of the use of coal mine gas would be greatly increased. In addition, emission credits and avoided penalties could substantially improve the economics of most coal mine gas projects, thereby stabilizing coal use for utilities. It is a still further object of this invention to provide a suitable means of transportation for recovered coal mine gas which partially uses the coal mine gas recovered as fuel for the transportation means.
Different methods have previously been devised to recover and transport the coal mine gas. For example, the 1982 patent issued to Hvizdos disclosed a Method and Apparatus for the recover and removal of natural gas from a mine by liquefying and collecting the gas within the mine and then transporting the liquified gas to the surface in a mobile tank. However, one drawback in the Hvizdos's method and apparatus is that it utilizes cryogenic liquid for condensing the coal mine gas. Such a cryogenic apparatus would be expensive to acquire and to use. It is a still further object of this invention to provide a method and apparatus for recovering coal mine gas without the necessity of using an expensive cryogenic super cooled liquid.
A major problem with the collection of coal mine gas is that methane cannot be economically collected for transport because the coal mines in which the gas exists are spread out over a large area. The large area would require miles of pipeline. However, existing utility pipelines cannot be used because the nitrogen and carbon dioxide levels in the methane gas are too high for pipeline gas quality. Further, methane will not liquify like propane gas unless it is frozen to 210 degrees below zero by use of cryogenics. As noted above, the cryogenic solution is quite costly.
While the use of existing pipelines is impractical, existing commercially available propane tankers could be modified to fit the needs of this particular industry. In order to utilize these existing propane tankers, certain modifications must be made to the tankers, most importantly including filling the tanker with activated carbons made from coal or commercial carbons not made from coal but with a high volumetric methane adsorption capacity. The activated carbons would adsorb the natural gas and make the gas transportation more economical.
In addition, if the methane is introduced into the propane tankers containing the activated carbons under preferred pressure conditions, the amount of methane that can be delivered would also make the method and apparatus economically viable. It is a still further object of this invention to provide an apparatus for transporting methane gas in modified propane tankers, which makes the transportation economically viable. Other and further objects of this invention will become obvious upon reading the below described Specification.